Abstract: The correlation between the impact energy of standard sized specimens and sub-sized specimens was investigated through series of Charpy V-Notch (CVN) impact tests on 20,16Mn and X70 steels at different temperatures ranging from -80 ℃ to 40 ℃. The ductile-brittle transition temperature (DBTT) of specimens with different sizes were also studied. All the results were contrasted to the ASTM and BS standards and a correction of the formula of the upper shelf impact energy was finally reached.